Fruit waxing method

ABSTRACT

A system for applying a coating of wax and fungicide to the surface of fruit applies the coating in two stages. The first stage sprays onto the fruit a mixture of both wax and fungicide, while a second stage sprays onto the fruit wax alone. The fungicide is thereby concentrated immediately adjacent the fruit, where it is most effective in controlling fruit decay, and the wax is at its full concentration at the outside of the coating, where it can provide an optimum surface shine.

This is a continuation of co-pending application Ser. No. 076,782 filedon July 23, 1987 and now abandoned.

BACKGROUND OF THE INVENTION

This invention relates generally to the application of wax to thesurface of fruit, and, more particularly, to the application of not onlywax, but also fungicide.

It is customary in the packing of fruit for shipment in cartons tocustomers such as retail grocers, to apply a coating of wax to the fruitsurface. This provides the fruit with a desirable shiny appearance,which is of particular importance with citrus fruit. It also iscustomary to include with the wax a fungicide for controlling fruitdecay. This is particularly important when the fruit are being shipped aconsiderable distance, such as across the country or overseas.

Fungicides used in the past for this purpose have typically been in aninsoluble powder form. This powder has been suspended in liquid wax byagitation in a mixing tank, and this liquid mixture has then beensprayed onto the fruit as the fruit is moved along a conveyor past aspray station. Thus, the wax performs the dual function of serving as abinder for the insoluble fungicide powder and providing the fruit withthe desirable shiny appearance.

Unfortunately, the fungicide and wax each tend to adversely affect theperformance of the other. That is, increasing amount of fungicide in theliquid mixture increases the control of fruit decay, but simultaneouslyreduces shine. Conversely, decreasing the amount of fungicide in themixture improves the surface shine, but reduces decay control. Thisproblem is accentuated when the fungicide is in insoluble powder form.

It should therefore be appreciated that there is a need for an effectivesystem for applying both wax and fungicide to the surface of fruit,which provides improved decay control while it simultaneously providesimproved surface shine. The present invention fulfills this need.

SUMMARY OF THE INVENTION

The present invention is embodied in an apparatus, and related method,for applying a coating of both wax and fungicide to the surface offruit, which provides not only enhanced control of fruit decay butsimultaneously provides an improved surface shine. The apparatusincludes conveyor means for transporting fruit along a path along withapplication means for applying both wax and fungicide onto the surfacesof the fruit, as they are being transported, to provide a surfacecoating of wax and fungicide. In accordance with the invention, thecoating applied to the fruit has a substantially higher concentration offungicide at its inside surface than at its outside surface, therebyproviding improved control of fruit decay while simultaneously providingimproved surface shine. These improved results can be achieved even whenusing reduced amounts of both fungicide and wax, thus leading tosubstantially reduced costs.

More particularly, the application means applies the coating to thefruit surfaces in two stages. In a first stage, a first liquid,consisting essentially of both liquid wax and fungicide, is sprayed ontothe fruit. Thereafter, in a second stage, a second liquid, consistingessentially of wax alone, is sprayed onto the fruit. Thus, in theresulting coating, the fungicide is concentrated immediately adjacentthe fruit surface, where it is most effective in controlling decay. Inaddition, the wax is at its full concentration at the outside of thecoating, where it is most effective in providing the desirable shinyappearance.

In an optional, more detailed feature of the invention, the first andsecond liquids can each include different waxes. Thus, the wax includedin the first liquid can be selected for its relatively low cost and forits properties in controlling fruit shrinkage and its effectiveness as abinder for the insoluble fungicide powder, while the wax included in thesecond liquid can be selected for its shine properties. The wax in thefirst liquid includes less expensive wax such as a wood resin wax,polyethylene wax or Carnauba wax, while the wax in the second liquid ispreferably a high-shine shellac wax.

Controlling the relative proportions of wax applied by the respectivefirst and second spraying stages also affects the degree of decaycontrol and surface shine the apparatus provides. Using the firstspraying stage to apply 60 to 90 percent of the total amount of waxapplied in the two spraying stages together, provides particularlyeffective decay control and surface shine. Preferably, 70 percent of thetotal wax is applied in the first spraying stage.

Other features and advantages of the present invention will becomeapparent from the following description of the preferred embodiment,taken in conjunction with the accompanying drawing, which illustrates,by way of example, the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWING

The FIGURE is a diagramatic view of an apparatus for applying both waxand fungicide to the surface of fruit.

DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference now to the drawing, there is shown an apparatus forapplying a coating of both wax and fungicide to the exterior surfaces offruit 11, particularly citrus fruit. The coating is applied to the fruitbefore it is packed in cartons for shipment to customers such as retailgrocers. The wax provides the fruit with a shiny surface appearance,which customers find desirable, and the fungicide aids in the control offruit decay, which can be a particular problem when the fruit is beingshipped across the country or overseas.

The wax and fungicide are sprayed in liquid form onto the fruit 11 byprimary and secondary overhead spray assemblies 13 and 15, respectively,as the fruit are moved along on a conventional brush bed conveyor 17.The direction of fruit travel along the conveyor is indicated by thereference numeral 19. This conveyor includes a succession ofclosely-spaced transversely-oriented cylindrical brushes 21 that allrotate in a forward direction, to advance the fruit past the sprayassemblies. Both sprayer assemblies spray liquids downwardly onto theportions of the fruit oriented upwardly and onto the conveyor brushes,which spread the sprayed liquid uniformly over the fruit surface.

The primary spray assembly 13 includes an elongated frame 23 orientedtransversely to the direction of fruit travel 19 and further includes anumber of nozzles 25 for spraying a primary liquid downwardly onto theconveyor 17 and the advancing fruit 11. In the depicted appratus, theprimary sprayer assembly frame is arranged to oscillate transverselyrelative to the conveyor so as to cover the conveyor's entire width.

The secondary sprayer assembly 15 likewise includes an elongated frame27 oriented transversely to the direction of fruit travel 19 and furtherincludes three sets of nozzles 29, 31 and 33 for spraying a secondaryliquid downwardly onto the conveyor 17 and advancing fruit 11. Thesecondary sprayer assembly is depicted as being of sufficient width tocover the entire conveyor without the need for any oscillatingtransverse movement.

In accordance with the invention, the primary liquid sprayed by theprimary sprayer assembly 13 includes both wax and fungicide, while thesecondary liquid sprayed by the secondary sprayer assembly 15 includeswax alone. As a result, the greatest concentration of fungicide occursat the inside of the coating, adjacent the fruit 11, where it mosteffectively can control fruit decay. In addition, the outside portion ofthe coating contains a full concentration of wax, thus providing animproved surface shine.

The wax that is sprayed by the primary spray assembly 13 is in liquidform, but the fungicide sprayed along with it is normally in aninsoluble powder form. A mixing tank 35 is therefore provided with meansfor agitating the mixture and suspending the fungicide uniformly in thewax. A primary pump 36 then pumps the agitated mixture through a conduit36a to the primary spray assembly, for spraying onto the conveyor 17 andfruit 11.

The wax that is to be sprayed by the secondary spray assembly 15likewise is in liquid form. A secondary pump 38 pumps the liquid from atank 37 through a conduit 38a directly to the secondary sprayerassembly, for spraying onto the conveyor 17 and fruit 11.

The relative amounts of wax applied by the respective primary andsecondary sprayer assemblies 13 and 15 can be selected so as to adjustthe degree of decay control and surface shine the apparatus provides. Ifa greater proportion of the total applied wax is applied by the primarysprayer assembly, improved decay control can be achieved, but withreduced surface shine. Conversely, if a lesser proportion of the totalapplied wax is applied by the primary sprayer assembly, decreased decaycontrol is achieved, but with improved surface shine. This, of course,presupposes a fixed concentration of the fungicide in the wax applied bythe primary sprayer assembly. In any case, the use of two sprayerassemblies in accordance with the invention can provide the same degreeof decay control and surface shine as is provided by prior waxingsystems, but with substantially reduced quantities of wax.

Tests have shown that applying 60 to 90 percent of the total wax usingthe primary sprayer assembly 13 leads to the most satisfactorycombination of decay control and surface shine for citrus fruit. Seventypercent is ordinarily the preferred level, although this percentage canvary according to the ripeness of the fruit 11 being coated.

Since the wax and fungicide coating is applied to the fruit 11 using twoseparate sprayer assemblies 13 and 15, the waxes applied by the twoassemblies can be of different kinds. The waxes, of course, must becompatible with each other.

The wax applied by the primary sprayer assembly 13 is preferablyselected on the basis of its cost as well as its properties in servingas an effective binder of the fungicide and in controlling fruitshrinkage. Using this criteria, carnauba wax or any other lower-shinewaxes such as wood resin and polyethylene waxes are preferred. Thesewaxes are usually available as a mixture with a shellac wax.

The wax applied by the secondary sprayer assembly 15 is preferablyselected solely for the surface shine it provides. High-quality shellacwaxes are preferred.

Many fungicides are suitable for use in the primary liquid sprayed bythe primary sprayer assembly 13. These include thiabendazole (TBZ) andbenomil, which are both available in powder form. A primary liquidincluding either of these two fungicides is opaque and, by itself, doesnot provide a good surface shine for the fruit. The two fungicides areordinarily used in concentrations of 3500-5000 ppm and 1500-2000 ppm,respectively, although these concentrations can vary according to thefruit's ripeness and the stage of the growing season.

A third suitable fungicide, imazalil, forms a translucent solution whenit is mixed with wax. When used in a concentration of about 2000 ppm,the resulting primary liquid can provide a good surface shine, evenwithout application of a further coating of wax alone. If desired, someamount of imazalil can be included in the secondary liquid sprayed bythe secondary sprayer assembly 15.

The spraying effected by the primary sprayer assembly 13 is controlledby a controller 39, via a control line 41. In particular, the controllercauses the spray nozzles 25 to spray the wax and fungicide mixturecontinuously onto the conveyor 17 and fruit 11 as the assemblyoscillates transversely relative to the conveyor. The assembly typicallyoscillates at a speed such that it completes one entire cycle in aboutthree or four seconds. This provides a substantially uniform spraycoverage across the conveyor's entire width. Alternatively, thecontroller can pulse the spray nozzles of the primary spray assembly ata selected rate and duty cycle.

The secondary sprayer assembly 15 is controlled by a pulse controller43, via three separate control lines 45, 47 and 49. Each separatecontrol line controls the pulsing of a separate set of spray nozzles 29,31 or 33, respectively. One set 29 includes three nozzles carried at thecenter of the assembly frame 27, and the other two sets 31 and 33 eachinclude two separate nozzles located at opposite ends of the frame.Separate solenoids are preferably located adjacent to each nozzle.

The controller 43 ordinarily pulses all three sets of nozzles 29, 31 and33 at the same rate and duty cycle. This rate and duty cycle areordinarily selected to be high enough to ensure that the brushes 21 ofthe conveyor remain continuously coated with wax. An operator (not shownin the drawing) can selectively cause one or both of the two side setsof nozzles 31 and 33 to spray additional wax onto the conveyor and fruit11 if he sees a higher than expected concentration of fruit near theconveyor edges.

The density or throughput of fruit 11 being moved past the sprayerassemblies 13 and 15 by the conveyor 17 is usually somewhat variable. Toaccount for this variation, it is usually desirable to correspondingmodify the rate at which wax and fungicide are applied by the primarysprayer assembly 13. The primary pump 36 is therefore adapted to pumpthe primary liquid at one of three different pressures (and thus flowrates), in accordance with the fruits' throughput.

A digital encoder 51 is therefore included to monitor the speed of abelt (not shown) that delivers fruit 11 to the apparatus. This encoderoutputs a signal on line 53 whose frequency is proportional to thebelt's speed. A pump controller 55 frequency divides the pulse signaland compares the resultant signal with several rate thresholds, todetermine which of several different speed ranges is occurring. Inaccordance with this determination, the controller outputs anappropriate pump control signal on line 57, to drive the primary pump 36at an appropriate speed. Thus, when the fruit are being delivered to theapparatus at a relatively high rate, the pump is operated at a highpressure and the primary spray assembly 13 sprays the primary liquid ata correspondingly high rate. Conversely, when the fruit are beingdelivered at a relatively low rate, the pump is operated at a lowpressure and the primary liquid is sprayed at a correspondingly lowrate.

It should be appreciated from the foregoing description that the presentinvention provides an improved apparatus for applying a wax andfungicide coating to the surface of fruit. By applying initially amixture of both fungicide and wax and, subsequently, wax alone, acoating can be provided with a higher concentration of fungicideadjacent to the fruit, where it is most effective in controlling fruitdecay, and with a maximum concentration of wax at the outside of thecoating, where it can provide an optimum surface shine.

Although the invention has been described in detail with reference tothe presently preferred embodiment, those of ordinary skill in the artwill appreciate that various modifications can be made without departingfrom the invention. Accordingly, the invention is defined only by thefollowing claims.

We claim:
 1. A method for applying a coating of wax and fungicide to thesurface of fruit, comprising steps of:transporting fruit along a path;first spraying onto the fruit being transported a first liquidconsisting essentially of both wax and fungicide; and second sprayingonto the fruit being transported a second liquid consisting essentiallyof wax; wherein the first and second spraying steps provide a coating ofwax and fungicide on the fruit surfaces, the coating having asubstantially higher concentration of fungicide at its inside surfacethan at its outside surface, thereby providing an effective control offruit decay while simultaneously providing an effective surface shine.2. A method as defined in claim 1, wherein the first and second liquidsused in the first and second spraying steps each include predominantlydifferent waxes.
 3. A method as defined in claim 2, wherein:the waxincluded in the first liquid includes a wood-resin wax, a polyethylenewax, or carnauba wax; and the wax included in the second liquid consistsessentially of a shellac wax.
 4. A method as defined in claim 1, whereinthe step of spraying the first liquid sprays an amount of wax between 60and 90 percent of the total wax sprayed in the first and second sprayingsteps.
 5. A method as defined in claim 4, wherein the step of sprayingthe first liquid sprays about 70 percent of the total wax sprayed in thefirst and second spraying steps.
 6. A method as defined in claim 1,wherein the step of spraying the second liquid includes a step ofindependently controlling a linear array of spray nozzles arrangedtransversely relative to the direction of fruit travel in the step oftransporting such that the spray nozzles located nearest each edge ofthe transported fruit and the spray nozzles located nearest the centerof the transported fruit spray selected amounts of the second liquid. 7.A method for applying a coating of wax and fungicide to the surface offruit, comprising steps of:transporting fruit along a path; firstspraying onto the fruit being transported a first liquid consistingessentially of both wax and fungicide, the wax including a wood-resinwax, a polyethylene wax, or carnauba wax; and second spraying onto thefruit being transported a second liquid consisting essentially of ashellac wax; wherein the step of spraying the first liquid sprays anamount of wax between 60 and 90 percent of the total wax sprayed in thefirst and second spraying steps; and wherein the first and secondspraying steps provide a coating of wax and fungicide on the fruitsurfaces, the coating having a substantially higher concentration offungicide at its inside surfaces than at its outside surface, therebyproviding an effective control of fruit decay while simultaneouslyproviding an effective surface shine.
 8. A method as defined in claim 7,wherein the step of spraying the second liquid includes a step ofindependently controlling a linear array of spray nozzles arrangedtransversely relative to the direction of fruit travel in the step oftransporting, such that the spray nozzles located nearest each edge ofthe transported fruit and the spray nozzles located nearest the centerof the transported fruit spray selected amounts of the second liquid. 9.A method of applying a coating of fungicide and wax to the surface offruit, comprising the steps of:spraying onto the surface of the fruit afirst liquid consisting of liquid wax within which an insolublefungicidal material in powdered form is uniformly suspended; and thensubsequently spraying onto the fruit a second liquid consistingessentially of wax the coating having a substantially higherconcentration of fungicide at its inside surface than at its outsidesurface, thereby providing an effective control of fruit decay whilesimultaneously providing an effective surface shine.
 10. The method asdefined in claim 9 wherein said wax contained in said second liquid isessentially a shellac wax.
 11. The method as defined in claim 9 whereinthe amount of wax deposited on the fruit from said first liquid is inthe range of 60 to 90 percent of the total amount of wax in the finalcoating, the amount deposited from said second liquid being in the rangeof 10 to 40 percent.
 12. The method as defined in claim 11 wherein theamount of wax deposited on the fruit from said first liquid is about 70percent of the total amount of wax in the final coating.
 13. The methodas defined in claim 9 wherein the fungicidal material is chosen from thegroup consisting of thiabendazole and benomil.
 14. The method as definedin claim 9 wherein the fungicidal material is thiabendazole in aconcentration in the range of about 3500 to 5000 parts per million. 15.The method as defined in claim 9 wherein the fungicidal material isbenomil in a concentration in the range of about 1500 to 2000 parts permillion.
 16. The method as defined in claim 9 wherein a conveyorincluding a succession of closely-spaced transversely-orientedcylindrical brushes that all rotate in a forward direction is utilizedto advance the fruit along a path, a primary overhead spray assemblydisposed above and extending transversely of said conveyor is utilizedfor spraying said first liquid onto the fruit as well as the conveyorbrushes, and a secondary overhead spray assembly disposed above andextending transversely of said conveyor is utilized for spraying saidsecond liquid onto the fruit.
 17. The method as defined in claim 16wherein said wax contained in said second liquid is essentially ashellac wax.
 18. The method as defined in claim 16 wherein the amount ofwax deposited on the fruit from said first liquid is in the range of 60to 90 percent of the total amount of wax in the final coating, theamount deposited from said second liquid being in the range of 10 to 40percent.
 19. The method as defined in claim 18 wherein the amount of waxdeposited on the fruit from said first liquid is about 70 percent of thetotal amount of wax in the final coating.
 20. The method as defined inclaim 16 wherein the fungicidal material is chosen from the groupconsisting of thiabendazole and benomil.
 21. The method as defined inclaim 16 wherein the fungicidal material is thiabendazole in aconcentration in the range of about 3500 to 5000 parts per million. 22.The method as defined in claim 16 wherein the fungicidal material isbenomil in a concentration in the range of about 1500 to 2000 parts permillion.
 23. A method of applying a coating of fungicide and wax to thesurface of fruit in order to protect the fruit from decay and provide itwith a shiny surface appearance, comprising the steps of:selecting aconveyor that includes a succession of closely-spacedtransversely-oriented cylindrical brushes that all rotate in a forwarddirection; placing the fruit upon said conveyor to advance the fruitalong a predetermined path; selecting a first liquid consisting ofliquid wax within which an insoluble fungicidal material in powderedform is uniformly suspended; selecting a second liquid consistingessentially of wax; selecting a primary spray assembly and placing itabove said conveyor and extending transversely thereof; selecting asecondary spray assembly and placing it above said conveyor andextending transversely thereof in downstream relation to said primaryspray assembly; utilizing said primary spray assembly for spraying saidfirst liquid onto the fruit and the conveyor brushes; utilizing saidsecondary spray assembly for spraying said second liquid onto the fruit;and controlling the rates at which said first and second liquids aresprayed onto the fruit such that about 60 to 90 percent of the waxcontained in the final coating is derived from said first liquid andapplied to the fruit by means of said primary spray assembly the coatinghaving a substantially higher concentration of fungicide at its insidesurface than at its outside surface, thereby providing an effectivecontrol of fruit decay while simultaneously providing an effectivesurface shine.
 24. The method as defined in claim 23 wherein said waxcontained in said second liquid is essentially a shellac wax.
 25. Themethod as defined in claim 23 wherein the fungicidal material is chosenfrom the group consisting of thiabendazole and benomil.
 26. The methodas defined in claim 25 wherein the fungicidal material is thiabendazolein a concentration in the range of about 3500 to 5000 parts per million.27. The method as defined in claim 25 wherein the fungicidal material isbenomil in a concentration in the range of about 1500 to 2000 parts permillion.